getServletConfig().getServletContext().getRealPath("/");获取路径，报空指针异常

2014-04-29 03:17:27 2.1k 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

Servlet核心机制与生命周期详解：从原理到Spring MVC底层的贯通在Java Web开发中，无论框架如何演进，Servlet始终是请求-响应模型的基础。理解Servlet的生命周期，掌握其单实例多线程的并发模型，是排查线上问题与应对面试的关键。HTTP协议本身无状态，因此会话管理借助Cookie与Session实现身份追踪，而Filter与Listener则为请求链路提供了统一的拦截与事件监听能力。这些底层机制不仅适用于传统Java EE应用，也是Spring MVC的核心——DispatcherServlet本质上就是一个增强的Servlet。从URL解析、请求参数处理阅读详情

需要到servlet里面获取项目路径，网上的方法都看了，全部都是报空指针异常，希望高手给个解决方案

package com.ccts.servlet;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import com.ccts.util.HibernateUtil;

public class MyFilter extends HttpServlet implements Filter {

public void doFilter(ServletRequest arg0, ServletResponse arg1,
FilterChain arg2) throws IOException, ServletException {
// TODO Auto-generated method stub
try{
//request 之前要处理的代码
HttpServletRequest request=(HttpServletRequest) arg0;
HttpServletResponse response=(HttpServletResponse) arg1;
HttpSession session=request.getSession();
String username=(String)session.getAttribute("loginuser");
if(username==null)//没有登录进行重定向
{
String filePath=this.getServletConfig().getServletContext().getRealPath("/");
System.out.println(filePath);
response.sendRedirect("/ccts/login");
return;
}
arg2.doFilter(arg0, arg1);
//response之后要要处理的代码

}
catch (Exception e) {
e.printStackTrace();
}
finally{
if(HibernateUtil.getSession()!=null){
System.out.println("session现在关闭");
HibernateUtil.getSession().close(); }
}

}

public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub

}
/**
* Constructor of the object.
*/
public MyFilter() {
super();
}

/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}

/**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here

}

}

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